Total white blood cell (WBC) count is the most widely accepted screening test for children at risk for occult bacteremia although its sensitivity is poor(27%-50%). Interleukin-8 (IL-8), an inflammatory cytokine, is a potent neutrophil activating protein and an early marker for increased total WBC count. This study examines whether plasma IL-8 is helpful as a screening test in assessing children at risk for bacteremia and to compare its sensitivity and specificity with those of the total WBC count. Eligibility criteria are : age 3-36 months, temperature >39.0 C obtained rectally; with either no focus of infection or with otitis media, non specific upper respiratory infection or pharyngitis; no antimicrobial agent or immunization within past 48 hours; onset of fever of >6 hours and <72 hours prior to presentation. For each subject, blood samples are drawn for culture and to measure plasma IL-8 concentrations and total WBC count. The upper limit of plasma IL-8 in healthy children is 30 pg/ml. Of the fifty-seven children enrolled since August, 1995, four (7.0%) had positive blood culture. Their plasma IL-8 levels were 6.6, 17.8, 66.1 and 190.0 pg/ml. Of the 53 culture negative children, plasma IL-8 levels ranged from 0.0 to 121.0 pg/ml (mean 16+25). While the sample to date is too small to draw conclusions about sensitivity, preliminary findings suggest that the specificity of IL-8 is comparable to that of total WBC and that plasma IL-8 levels in the emergency department may be useful in predicting occult bacteremia in febrile children. In order to yield a sufficiently large sample to estimate sensitivity of plasma IL-8 levels, study recruitment continues.